1. Field of the Invention
This invention relates to a method and a system for determining a heating point and a heating line in the bending of a steel plate. More specifically, the invention relates to the method and system useful for application to the bending of a steel plate having complicated curved surfaces, such as an outer panel of a ship hull.
2. Description of the Prior Art
The outer panel of a ship hull is composed of a steel plate about 10 to 30 mm thick with a complicated undevelopable curved surface which reduces propulsion resistance for efficient navigation in the water. To form this curved outer panel, a processing method generally called line heating has been known for long. This method heats the surface of a steel plate locally by means of a gas burner or the like, to cause the extraplane angular deformation or intraplane shrinkage deformation of the steel plate due to plastic distortion, and skillfully combines these deformations to obtain the desired shape. This method is used at many shipyards.
FIG. 1 is an explanation drawing conceptually showing an earlier technology concerned with a method for bending a steel plate to serve as an outer panel of a ship hull. FIG. 2 is a front view showing a wooden pattern for use in the bending in a state in which it is mounted on the steel plate. As shown in both drawings, according to the earlier technology, many (10 in the drawing) wooden patterns 1 following frame lines of the outer panel of the ship hull (lines extending along frame materials for the outer panel at positions where the frame materials are attached; the same will hold in the following description) as target shapes are mounted on a steel plate 2. Then, an operator compares the shapes of each wooden pattern 1 and the steel plate 2 by visual observation, and considers differences between their shapes, e.g., the clearance between the wooden pattern 1 and the steel plate 2. Based on this consideration, the operator studies what position to heat in order to bring the steel plate 2 close to the target shape. As a result, the operator determines each heating position (heating point). Concretely, the wooden pattern 1 is rolled along the frame line of the steel plate 2 in a vertical plane (the same plane as in FIG. 2). The points of contact of the wooden pattern 1 with the steel plate 2 during the rolling motion are watched to determine the heating points in consideration of the clearance between the wooden pattern 1 and the steel plate 2 in each state.
Then, it is considered how to connect the respective heating points together in order to make the steel plate 2 similar to the target shape. Based on this consideration, a heating line is determined. As shown in FIG. 3, heating lines 3 that have been determined are marked on the surface of the steel plate 2 with chalk or the like, and the steel plate 2 is heated with a gas burner along the heating lines 3.
With the earlier technology as described above, the steel plate 2 is heated with a gas burner by the operator along the heating lines 3 determined by the operator's sense based on many years of experience. As a result, a predetermined curved surface is obtained. Acquiring the ability to determine the heating lines 3 rationally is said to require more than about 5 years of experience. This has posed the problems of the aging and shortage of experienced technicians. The bending procedure also takes a large amount of time for incidental operations, such as the production, mounting and removal of the wooden pattern 1 for the steel plate 2, thus lengthening the entire operating time.
To solve the problem of the shortage of experienced technicians and reduce the operating time, it is necessary to improve, theorize and automate the bending operation while taking into consideration know-how that operators acquired through experience.